1. Field of the Invention
The present invention relates, generally, to fireproof or fire retardant laminations for use in electronic or electric devices. The present invention also relates to methods for fabricating such laminations.
2. Description of the Prior Art
Numerous processes are recognized in the art for the manufacture of laminations having a utility in electronic or electric devices. Conventionally, a substrate has typically been impregnated with a formol-phenolic type of thermosetting resins, the impregnation being conducted in one or two depository applications of the resin to a, e.g., cellulosic substrate. When the process is characterized as being conducted in two applications, the first impregnation step typically makes use of a relatively low viscosity conventional phenolic resole. The impregnated substrate is then usually steamed to eliminate solvents, and to yield a specific degree of condensation of the resin. Subsequently, a number of sheets, or lamina, are then placed together and pressed at high temperature to yield the desired lamination.
Laminations of these varieties, based upon phenolic resin impregnated paper, are widely utilized in, for example, electrical home appliances, automobiles, children's toys, and the like. In these applications, fireproofing the devices is usually highly desirable, if not mandatory. Typically, fireproofing is accomplished by incorporating into the laminations phosphate esters of aryl, salts and acid derivatives of phosphorous, chlorinated paraffins, brominated aryl derivatives, antimony trioxide, and the like.
In order to effectively rate the fire retardant or fireproof characteristics of these laminations, the Underwriters' Laboratory has established the classifications V0 or V1 in accordance with "UL Subject 94". These tests require the vertical displacement of a sample of 12.7 mm above a Bunsen burner having a 9.5 mm diameter. The distance between the lower edge of the sample and the burner is set at 9.5 mm, and the blue flame of the burner regulated to a height of 19 mm. The flame is maintained for 10 seconds beneath the lower extremity of the sample, and the duration of flame persistency for the first heating noted; the burner is then returned a second time for 10 seconds and the flame persistency for the second heating being noted again. This is repeated with five samples; the total flame persistency must be less than 50 seconds for the V0 classification, and less then 250 seconds for that of V1.
The need to render the laminations employed in electric or electronic devices flameproof is not the only substantial consideration with regard to the desirable physical and chemical features thereof. In addition, the laminations must also possess numerous other characteristics including a resistance to trichloroethylene and a resistance to the absorption of water, be suitable for punching, and have good translucent properties. In order to imbue the laminae with satisfactory punching characteristics, to facilitate fabrication of various devices therefrom, it has been found indispensable to plasticize the phenolic resins. However, in order to yield an article capable of meeting the V0 and V1 classifications of the Underwriters' Laboratory, the substrate, typically paper or other cellulosic materials, must include considerably large quantities of fireproofing agents and adjuvants. While it is conceivable to balance the two afore-mentioned characteristics, optimization of the amount of plasticizer necessary for cold punching the laminae and the amount of fireproofing agents necessary for a V0 classification materially alter the remaining characteristics in a very depreciating sense. That is, this optimization yields a low resistance to trichloroethylene, a rather pronounced tendency for the absorption of water, and a severe diminishment of insulation resistance. Because of this, it is currently impossible to produce laminations which will meet either the V0 or V1 classification and which also are possessed of other very desirable characteristics.
Accordingly, the need exists to provide laminations for electric or electronic devices, which laminations are fireproof in the sense that they can meet the requirements of either V0 or V1 testing, and which are nonetheless possessed of the remaining desirable features ennumerated above. The need also exists to provide a method to produce such laminations, which method is simple, efficient, and economical, from a commercial point of view.